This is a talk I've been working on for a while. It starts off motivating why you might want to write compute shaders (tl;dr you can exploit the impressive compute power of GPUs but portably), then explains the basics of how, including some sample code to help get people started.
Slides: https://docs.google.com/presentation/d/1dVSXORW6JurLUcx5UhE1...
Sample code: https://github.com/googlefonts/compute-shader-101
Feedback is welcome (please file issues against the open source repo), and AMA in this thread.